Combustion in well with steel liner



March 17, 1959 H. L Pr-:Lzr-:R ETAL 2,877,847

COMBUSTION IN WELL WITH STEEL LINER Filed Sept. 2S. 1955 k/pa iR 0rOXYGEN INERTS WSECONDARY GAS for MIXING ond COLING *l o N a m m v f E gmn N J. n 2 1 A x m.. I R R um r 2 1 E M f l u C ,d a P M. r L. m m n mmf l .e A M y y s M W. E Mw N 2 5 W /f f z/ z/ n kw \\\T l f \\N \\\\\NN\N uN CCNSQMDATED -l PRDUClNG' 2,877,847 Patented Mar. 17, 1959 coMBUsnoN1N WELL wim STEEL LINER Harry Louis Pelzer, Catoosa, and Raymond M.Carr, Tulsa, Okla., assgnors to Sinclair Oil Gas Company, Tulsa, Okla.,a corporation of Maine Application September 26, 1955, Serial No.536,670

5 Claims. (Cl. 16S-39) This invention relates to a process for therecovery of oil and gas from subterranean formations. More particularly,the present invention is concerned with a process for the recovery ofthe oil and gas by thermal recovery means from subterranean oil bearingformations characterized by an unconsolidated structure or friablestructure such as is indigenous to California.

It is well known that the recovery of oil from subterranean formationsis in general an incomplete process. It is further known that energyinput is required to bring oil into a well bore from remote portions ofa bearing formation. Practices adapted to raise the percentage recoveryof oil from a given formation have included repressuring, such as by gasand air, mechanically pumping and water ooding. Another method ofrecovery comprises the establishment of and propagation of a heat wavewithin a producing formation from an input well as a means forrecovering components thereby driven to an output well. A particularlyadvantageous method incorporating the heat wave principle is shown inthe patent art by the Smith et al. Patent No. 2,642,943. The presentinvention relates in particular to a process which is adapted to employthe heat wave type recovery process such as that of the Smith et al.patent.

The present invention is predicated on the fact that known methods ofestablishing heat waves in underground formations are inadequate whendealing with oil bearing strata comprising unconsolidated sands orfriable structures. In a well located in unconsolidated strata it isnecessary to keep the well casing and liner in place to avoid collapseof the bore walls. In many cases it is even necessary to gravel packaround the liner to avoid movement of sands into the bore through theliner slots provided for passage of oil or gas or their mixtures intothe bore. Thus, in establishing and propagating a heat wave from aninput well in unconsolidated sands, the casing and liner must remain inplace to support the bore hole walls. The same is true in friable rockstrata which, although consolidated, can move or collapse due to variousforces such as heat and pressure. The method of the present invention isconcerned with establishing a heat wave in a formation in such rockstrata with the casing and liner in place in the bore hole generallyopposite the strata in which the heat wave is to be established. Themethod is also applicable in establishing a heat wave in strata whichhave no particular tendency to move or collapse; however, the advantagesderived by having a liner opposite the producing formation andestablishing the heat wave with the liner in place would not normally besucient to justify the extra expense and care necessary in the presentmethod over the use of the conventional manner of establishing the waveby firing the well opposite a bare formation. In the method of directlyring a well bore, burner exhaust gas temperatures of about 1200 to 2000F. or more are generally obtained which sometimes is effective incleaning an adjacent formation resulting in increased permeabilitythrough carbon burn-out; however, the use of such ternperatures within aliner in establishing a heat wave across a lined bore would cause unduedeformation and oxidation of the steel liner and cave-in of the wellbore.

The initial heating of strata to establish a heat wave surrounding abore hole with the liner in place is accomplished according to th'epresent invention at certain defined conditions of temperature andactivity of the atmosphere present. Upon establishment of a heated areain this manner, the heated portion of the unconsolidated sands must bemoved away from the bore hole and a heat wave established at a distancefrom the bore hole under conditions such that it is relatively cool inand immediately adjacent the bore hole. The heat wave can then bepropagated and otherwise run to completion in any manner desired butpreferably by the process described in the Smith et al. patentabove-identified and the process described in the co-pending applicationof' Pelzer, Serial No. 414,489, tiled March 5, 1954.

The present invention thus is a method for the recovery of oil and gasfrom oil bearing underground formations through establishing a heat wavefrom an input well with a liner opposing the strata of propagation andparticularly where the formation or strata of propagation ischaracterized by an unconsolidated nature or by a structure which willresult in unconsolidated materials upon the application of heat,pressure or other extreme conditions, i. e. friable sands. The processis effected by establishing a heated zone of formation surrounding theinput well in a manner so that the temperature of the gases entering thestrata heat the well casing and the immediately adjacent sands to atleast about 650 F. but not over about 900 F. At these high temperaturesit is essential that no substantial amount of free oxygen, e. g. notgreater than about 2 volume percent, be present in the gases contactingthe liner and passing into the adjacent formation. These gases are inertto combustion and will include carbon dioxide, fuel gas, methane,nitrogen, etc. and as indicated no or only small amounts of oxygen.Although we prefer substantially no free oxygen in these gases, thepermissible amount of oxygen which can be tolerated is variable anddepends primarily upon temperature and character of carbon deposits inthe adjacent strata. Care should be observed to avoid conditions whichare substantially deleterious to the liner and/or which would oxidizesufcient carbon in the formation adjacent the liner to raise the linertemperature above about 900 F. Heating under such conditions is continued until a heated zone is established which extends radially fromthe hole.

When the heated zone is obtained, burning within the liner isdiscontinued by discontinuing the supply of air or other oxygen supply.The bore hole and the immediately adjacent strata are at a temperatureof at least about 650 F. and preferably below about 900 F. After coolingthe bore hole and adjacent strata to below about 400 to 650 F., as bypassage of inert gases of the type described into the strata, acombustible mixture of gases is passed into the formation. Thecombustible gases must be below about 650 F., and preferably below about400 F., and, for example, can be unheated to .exert a cooling eect sothat upon passing through the well bore liner and the immediatelyadjacent strata they effect a further cooling of the well bore liner,casing and strata by heat transfer to the gases. Upon reaching thefrontal area of the heated zone the gases are of sufiicient temperatureto ignite and initiate and maintain the heat wave.

The distance the heated zone will extend from the bore at the conclusionof the heating step can vary widely. This zone will in all cases be wideenough so that the cooling gases will not unduly dissipate the heat waveor front while cooling down the bore hole and immediately adjacentstrata. Actually the cooling gases move the heat wave outwardly from theinput well and until combustion gases are introduced the cooling gaseswill exert a temperature reducing effect towards the heat front. Whenthe bore hole is cooled to less than about 650 F., or less than about400 F., as the case may be, and suicient of the adjacent strata is alsocooled to avoid carbon disposed tubular member 22. An oxygen-containinggas burn-out which `would raise the liner temperature above about 650F., the combustion gases are introduced to propagate the 'heat wave andrecover oilor gas or their mixtures from the output well. Thus, thewidth or radius of the heated wave will provide for a sufiicient coolingzone and yet after cooling the wave must be hot enough to supportcombustion. During the heating step it is advantageous to obtain the 650to 900 F. temperature for at least about a five foot radius from thebore hole and preferably at least about ten feet. Cooling gases arepreferably introduced until the liner and at least about the adiacentthree feet of strata are cooled below about 650 F. and preferably belowabout 400 F.

The invention will be described further by reference to the attacheddrawing in which Figure l shows a well bore in communication withunconsolidated producing sands of the type described partly in sectionand partly in elevation and shows one type of burner apparatus(schematic) and liner which can be used with advantage in practicing thepresent invention; and

Figure 2 is a typical live-spot pattern of input and output wells.

Referring now to the drawing, the numeral 10 represents the earthssurface through which an input well bore 12 has been drilled to providecommunication with oil-producing formations 14. A pluralitr of outputwells 12a are provided in spaced relation with the input well, as in alive-spot pattern, see Figure 2, to facilitate recovery of materialsfrom the strata. The unconsolidated nature of the producing stratarequires the use of liners 16 opposite the strata and casing 17 whichextend above and below the producing strata. Liners 16 are, in general,cylindrically-shaped members characterized by shape and size to tsomewhat snugly within a bore hole and close ofi the bore hole from theunconsolidated sands. This may be accomplished with standard liners byutilizing packing means such as gravel (not shown) and serves to preventsands from entering the bore hole and interfering with production. Thisis especially important in view of the fact that oil bearing formationscomprising unconsolidated sands generally occur at a plurality ofvertically spaced points at any given area or are o such great thicknessthey are treated as being a plurality of strata. For eticient productionunder such circumstances communication with all of the producing stratamay be effected. However, the filling of a bore hole by sands pouringinto it from a higher producing strata obviously would bedisadvantageous. To prevent this,. liners such as members 16 have foundwide use. Where liners are cemented in place, conventional expansionjoints (not shown) are used in practicing the present invention as thetemperature reached may be damaging. Liners 16 are provided withslot-like apertures 18 to provide the necessary controlled communicationof the well bore with the strata.

Disposed within the bore hole 12 to a distance extending to immediatelyabove the slotted portion of a liner is a secondary casing member 20. Anadditional tubular member 22 is disposed centrally within casing member20. An igniting means, such as indicated by numeral 24, advantageouslyis employed and disposed, for example, et the lower extremity of thecentral tubing member 22. The numeral 25 represents a thermocouple orother ternperature indicating means provided to follow down holetemperatures. To establish the heated portion of the strata inaccordance with the present invention a fuel such as natural gas or alow molecular weight'hydrocarbon gas, for example methane, is passedfrom the earths surface to the burner area through the centrally ispassed to the burner area through the annular space 27 defined bytubular members 22 and 10. As the fuel and oxygen mix in the presence ofthe actuated igniter means 24, burning occurs with concomitant releaseof heat. A secondary gas is passed into the well bore simultaneouslywith the air and fuel in the annular space 29 defined by casing members20 and 17. The secondary gas mixes with the hot combustion productsproduced by the burning of the fuel and serves to dilute i. to cool thegases to the point, i.e. below about 900 F., where they can be permittedto enter liner slots 18 and thus the formation. To facilitate thismixing, a mixing space 30 can be pro vided between the burner area andliner slots; generally a space of about 2 to 3 feet or more is adequate.

In heating the strata about the well bore, about 40 to 60 parts ofsecondary gas can be used for each part of fuel burned in order to coolthe combustion products from their high temperature, i. e. about 4000uF., to the desired temperature, that is, a minimum of about 650 F. and amaximum of about 900 F. The quantity of fuel employed and the quality ofthe oxygen-containing gas and of the secondary gas are such that nosubstantial free oxygen is permitted to exist between the generalburning area and the liner slots previously described. This isaccomplished to advantage by employing slightly less oxygen than thestoichiometric quantity necessary for complete combustion ot the primaryfuel. By this procedure, all of the free oxygen will be combined andconverted to an inert form. By limiting the maximum temperature to about900 F. and having substantially no oxygen present, lampblack formationand oxidation of the metal liner will not normally occur. If conditionsobtaining are such that lampblack formation can occur at 900 F. andbelow, it may be desirable to operate under conditions such that nounburned fuel contacts the liner at temperatures above about 400 to 600F.

The cooling step which follows immediately upon establishing suiicientheated area about the well bore is effected by the use of inert gases,for example, low molecular weight hydrocarbon gases or nitrogen orcarbon dioxide or other inerts which do not contain substantial freeoxygen. By inert gases is meant a gas or mixture of gases having acomposition which is not combustible under the conditions encountered.While it is possible to employ gases containing small quantities ofoxygen, for instance up to about 2 percent, during the cooling step thiscan occur only when the conditions defined by the nature of carbonaceousmaterials in the strata adjacent the well bore and temperatures are suchthat undue burning or temperature rise does not occur. Whilerecognizingthis possibility of use of small quantities of oxy gen weprefer to avoid the presence of oxygen as it does not contribute tocooling in any unique or necessary manner and can possibly complicatematters 'oy eecting combustion and resulting in temperature rise.Cooling can be accomplished by cutting off the supply of fuel andoxygencontaining gas while continuing to supply secondary gas to thesystem and is continued until the well bore liner and the immediatelyadjacent strata are cooled to a temperature of say below about 650 F.and preferably below about 400 F. At this point, as a generality, it ispossible to introduce a combustible mixture without effecting combustionat the liner or in the first several feet of cooled strata. Thiscombustible mixture to advantage is at a temperature below that of thestrata immediately adjacent the well bore so that further cooling isaccomplished by its passage and heat utilization is more eficient as aresult of the heating ofthe combustible mixture as it passes through thestrata to the heat wave front. By combustible it is meant a freeoxygen-contain ing gas, advantageously containing from about 2 to 6volume percent of oxygen, which, upon contact with the heat wave frontalarea at the temperature occuring there, will burn thereby raising thetemperature so that with further quantities of the gas it is capable ofetfecting burning of residual carbonaceous materials remaining in thestrata at that point, that is, materials unmoved by the inlluence of theprevious thermal drive effected in heating the strata. As the wave isnow removed from the general area of the well bore the. temperature canbe permitted to rise and a heat wave, for example, in the sense of theSmith et al. process or the Pelzer process previously identified can bepropagated.

In practicing the invention, an input well and at least one output wellare provided for communication with the oil bearing formation. Existingwells can be used though it is frequently more advantageous to drillspecial wells for practicing the invention since the spacing desired canthen be obtained with greater ease. The wells are cased in the mannerwhich is usual for formations of the type under consideration with slotsbeing provided in the liners at formation level. Heat is then introducedinto the strata to establish the first heated zone previously described.Heat can be introduced by burning gases at the earths surface andpassing the heated combustion products into the well bore and into theformation; or, and preferably, heat can be supplied by burning a fuel inthe well bore at approximately formation level by use of a burner andigniter apparatus in the manner described above.

Employing a burner and igniter apparatus, sufficient concentric pipesare placed within the well to provide two separate annular spaces and acentral conduit. A thermocouple or other temperature indicating meansand an igniter means, each with the necessary leads, are lowered throughthe central conduit. Fuel, e. g. methane or natural gas, is passed intothe well bore through the central conduit while air, or other freeoxygen-containing gas, and a secondary mixing gas such as a flue gas arepassed into the well bore separately through annular spaces as have beendescribed. A primary gas containing about 50 to 90 B. t. u. per cubicfoot of mixture normally is sufficient to provide the necessary heat. Atypical concentration of fuel, air and secondary gas mixture which canbe used contains about 2 percent fuel and 4 percent oxygen. Otherconcentrations can, of course, be ernployed providing all free oxygen isconsumed and suflcient secondary gas is present to cool the combustionproducts to at least as low as 900 F. before they contact the liner andstrata. After ignition has begun the igniter apparatus can be withdrawnslightly to prevent damage to it while the thermocouple is permitted toremain in the llame; a separate thermoconple in contact with the linercan be employed to follow liner temperatures if desired. After suicientburning has been effected to heat the strata radially for say feet,which normally occurs in about 3 to l0 days or more, fuel and airintroduction are stopped while the supply of secondary gas is .continuedto cool the well bore, casing and the first few feet, e. g. 4 feet, ofthe heated zone.

The well bore and the first few feet of formation are cooled, i. e. tobelow about 650 F. and preferably below about 400 F., in about 12 to 36hours when using the secondary gas as coolant. Combustion within thestrata is then'initiated by passing unheated oxygen-containing gases andfuel into the strata from the well bore being careful to avoid use ofexplosive mixtures where low molecular weight hydrocarbons are used asfuel. A mixture containing about l0 to 40 or more B. t. u. per cubicfoot of air normally is sufficient to widen and move the heated annularheat wave in the formation. The cold gas mixture further cools the bore,liner and strata. while becoming heated and upon reaching the front ofthe heated zone is at sufficient temperatures to ignite spontaneously,thereby further heating the strata at the wave front. This burning iscontinued by continuing the supply of air and fuel; when the temperaturein the wave is suflcient to permit burning the residual carbonaceousmaterials of the strata, fuel supplyto the strata can be discontinued ifdesired. Oxygen supply is, of course, continued so long as themaintenance and propagation of the heat wave is desired, or until suchpoint that the heat wave can be completed by switching to an in situsteam drive effected by passing water into contact with the wave in themanner described in the Pelzer application.

Frequently, as noted above, unconsolidated producing sands are of greatvertical width or occur on a plurality of levels or both. The presentinvention can be practiced under such circumstances simply byestablishing heat waves in the manner described in one area or formationat a time, packing it ot from outside communication (in the input well)except for supply of the propagation gases and then performing theprocess on the next formation or zone. For this purpose the igniterapparatus can be adapted to move vertically in the well bore so that itcan be placed at the formation desired. Alternatively, a large sectionof the lined bore hole can be heated and then cooled through lowering ofthe burner apparatus and then propagation of the wave effected throughthe treated section.

What is claimed is:

1. In a method for the recovery of oil and gas from an oil bearingunderground formation having a steel liner adjacent a strata in which aheat wave is to be propagated wherein an input well providescommunication with the bearing formation and recovery of products iseffected by establishing and propagating a heat wave within theformation, the method of establishing a heat wave which comprisesestablishing a heated zone of strata about said input well by passingsubstantially inert gases heated to an elevated temperature of at leastabout 650 F. but not in excess of about 900 F. from said input well borethrough said liner and into said formation, then cooling said input wellbore and a portion of the heated zone of formation immediately adjacentsaid input well in the absence of a substantial amount of free oxygenand until the temperature of said input well and a portion of theimmediately adjacent formation is below about 650 F. and thenestablishing and propagating a heat wave within said formation bypassing an oxygen-containing combustion gas into said input well andinto said formation to the heated front of said formation and burningcombustibes there.

2. The method of claim 1 in which said heated inert gases are obtainedby burning a fuel with air containing not more than a stoichiometricquantity of oxygen and the resulting combustion products are mixed withsuthcient secondary gas to result in a gaseous mixture of the desiredtemperature.

3. The method of claim l in which the temperature of cooling is belowabout 400 F.

4. 'The method of claim 3 in which the initially-heated zone extendsradially from said input well for at least about tive feet and thecooled portion of the formation is at a temperature of below about 400F. and extends radially from said input well for at least about threefeet while leaving a heated front hot enough to support cornbustion ofthe oxygen-containing combustion gas passed into the formation.

5. The method of claim 3 in which the initially-heated zone extendsradially from said input well for at least about ten feet and the cooledportion of the formation is at a temperature of below about 400' F. andextends radially from said input well for at least about three feetwhile leaving a heated front hot enough to support combustion of theoxygen-containing combustion gas passed into the formation.

References Cited in the tile of this patent UNITED STATES PATENTS2,506,853 Berg et al May 6, 1950 2,642,943 Smith June 23, 1953 2,668,592Piros et al. Feb. 9, 1954 2,788,071 Pclcr-- -.,t. Apr. 9, 1957

1. IN A METHOD FOR THE RECOVERY OF OIL AND GAS FROM AN OIL BEARINGUNDERGROUND FORMATION HAVING A STELL LINER ADJACENT A STRATA IN WHICH AHEAT WAVE IS TO BE PROPAGATED WHEREIN AN INPUT WELL PROVIDESCOMMUNICATION WITH THE BEARING FORMATION AND RECOVERY OF PRODUCTS ISEFFECTED BY ESTABLISHING AND PROPAGATING A HEAT WAVE WITHIN THEFORMATION, THE METHOD OF ESTABLISHING A HEAT WAVE WHICH COMPRISESESTABLISHING A HEATED ZONE OF STRATA ABOUT SAID INPUT WELL BY PASSINGSUBSTANTIALLY INERT GASES HEATED TO AN ELEVATED TEMPERATURE OF AT LEASTABOUT 650*F. BUT NOT IN EXCESS OF ABOUT 900*F. FROM SAID INPUT WELL BORETHROUGH SAID LINER AND INTO SAID FORMATION, THEN COOLING SAID INPUT WELLBORE AND A PORTION OF THE HEATED ZONE OF FORMATION IMMEDIATELY ADJACENTSAID INPUT WELL IN THE ABSENCE OF A SUBSTANTIAL AMOUNT OF FREE OXYGENAND UNTIL THE TEMPERATURE OF SAID IMPUT WELL AND A PORTION OF THEIMMEDIATELY ADJACENT FORMATION IS BELOW ABOUT 650*F. AND THENESTABLISHING AND PROPAGTING A HEAT WAVE WITHIN SAID FORMATION BY PASSINGAN OXYGEN-CONTAINING COMBUSTION GAS INTO SAID INPUT WELL AND INTO SAIDFORMATION TO THE HEATED FRONT OF SAID FORMATION AND BURNING COMBUSTIBLESTHERE.